An important activity in industrial manufacturing processes is the taking of precise measurements of patterns, machine components, workpieces, locations of holes and/or studs and the like. In particular, when individual components are manufactured at different locations and assembled together at a final assembly shop, proper alignment of said components is critical. Accuracy in fitting these components together makes it possible to avoid reworking and modifications. Furthermore, when individual components do not properly align, identification of the root cause of the misalignment is important for the analysis and correction of the problem.
Providing holes, studs and abutment surfaces in proper, precise locations on tooling, machine components, automobile frames, and the like is normally accomplished using a reference system such as a tool and ball system or a line of sight system. In each of these reference systems, a sighting target is positioned on special tooling and instruments are used to determine proper, precise locations of holes, studs and/or abutment surfaces with respect to such targets.
Using conventional coordinate measuring machines a hole position, threaded or otherwise, is typically described by selecting three points on the surface adjacent to the hole which is used to create a plane, and the hole axis vector. Three points are then selected in the hole to create the hole axis. The intersection of the hole axis along the vector at the plane then describes the center point of the hole on the surface. This method is subject to operator error and obstruction issues. At times a gauge is inserted into the hole and this provides an easier means of picking or selecting points on a cylinder parallel to the hole axis.
With surface scanning equipment, the inner surface of a hole or the outer surface of a stud can be scanned. From the scanned data, a surface and cylinder can be constructed and the intersection of the surface and the constructed cylinder axis can be used to determine a measurement point. This method is tedious but can yield accurate positional measurements. Furthermore, this method cannot be used on any fastener without a direct line of sight.
Using photogrammetry a similar procedure is undertaken where three points are selected on the surface near the hole in question to produce a plane and the hole edge is determined via contrast in measurement images. This method becomes less accurate as the contrast between the edge and the background data is reduced. Accuracy is also reduced as the angle of incidence for the measurement image increases, becoming essentially useless as the angle approaches 40 degrees. Furthermore, this method cannot determine the position of holes which are obstructed by other features of the object being measured. In many cases a target can be inserted into the hole thus allowing a direct measurement, however accuracy is again degraded as the angle of incidence increases and is useless if the hole is obstructed. Advanced computer-aided systems are typically utilized in the above referred to reference systems.
In the advancement of the above described measurement systems, advanced computer-aided photogrammetry has been utilized as a measurement tool for determining specific locations on industrial devices and equipment. Light-reflective or contrasting targets are positioned at predetermined locations on specialized tooling in accordance with a prearranged pattern, thus allowing the precise relationship of the pre-selected locations to be measured and/or verified. However, placing contrast or reflective targets at the pre-selected locations can be a burdensome and time-consuming task. For example, if a contrast target is affixed to a flange that is welded to a bolt used to screw into a threaded hole, tightening of the bolt to secure the contrast target to the hole forces the contrast target to rotate as the bolt is tightened, and could position the contrast target in an undesirable location or interfere with obstructions while being rotated to engage the threads. Therefore, there is a need for specialized tooling that will allow a user to secure a contrast or reflective target relative to a desired location and yet provide freedom of movement such that the target location can be positioned as desired.